Recent studies have emphasized the limitations of conventional coronary angiography. These limitations include the - large intraobserver and interobserver variability that result from subjective visual grading of coronary stenotic lesions. Furthermore, pathologic findings have shown a lace of correlation between the severity of coronary stenosis as estimated from coronary angiograms and the actual severity of stenotic lesions measured in postmortem hearts. As a result, more physiological means of assessing coronary artery stenosis are being investigated. One parameter that has been suggested is the coronary flow reserve (CFR). Parametric flow imaging techniques utilizing digital subtraction angiography (DSA) have been proposed as a means of measuring CFR. One of the limitations of these parametric imaging techniques is the fact that they are capable of measuring only relative coronary flow rates. Therefore, they can not detect complicating factors such as elevated baseline coronary blood flow. Also, there have been recent reports that factors other than stenosis, such as perfusion pressure, may affect CFR. In addition, one of the greatest clinical problems of using temporal subtraction technique in the human cardiac catheterization laboratory for parametric imaging flow measurement has been reponed to be the motion misregistration artifacts. The purpose of this research plan is to develop and apply in patients a phasic volumetric coronary blood flow measurement technique utilizing a motion immune dual-energy digital subtraction mode. More specifically, the aims are: (l) investigation of the physical and physiological parameters affecting absolute volumetric blood flow measurement. (2) investigation of the hypothesis that real- time dual-energy subtraction in conjunction with the first pass distribution analysis can be utilized to measure phasic volumetric coronary blood flow accurately. The measurement will be performed on tissue subtracted dual-energy (as opposed to temporal subtraction) images and will produce absolute (as opposed to relative) volumetric blood flow measurement (3) Investigation of the hypothesis that the ratio of phasic hyperemic coronary blood flow rate and its perfusion pressure is a reliable quantitative measure of coronary stenosis severity. (4) Investigation of the hypothesis that the ratio of hyperemic diastolic to systolic flow rates is a useful parameter in assessing the stenosis severity. (5) Implementation of the absolute coronary blood flow measurement technique for human studies in the cardiac catheterization laboratory. The results of this research will provide improved physiological methods of quantitating coronary artery stenosis severity in patients, using dual-energy digital subtraction angiography. The motion immune dual-energy system can be implemented with minor modification of the existing instrumentation in a cardiac catheterization laboratory. This quantification technique could be used to measure absolute phasic coronary flow and flow reserve in every patient undergoing radiographic studies.